netfs: Add support for DIO buffering

Add a bvec array pointer and an iterator to netfs_io_request for either
holding a copy of a DIO iterator or a list of all the bits of buffer
pointed to by a DIO iterator.

There are two problems:  Firstly, if an iovec-class iov_iter is passed to
->read_iter() or ->write_iter(), this cannot be passed directly to
kernel_sendmsg() or kernel_recvmsg() as that may cause locking recursion if
a fault is generated, so we need to keep track of the pages involved
separately.

Secondly, if the I/O is asynchronous, we must copy the iov_iter describing
the buffer before returning to the caller as it may be immediately
deallocated.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org

diff --git a/fs/netfs/objects.c b/fs/netfs/objects.c
index 1bd20bdad98361f941f49593db9072d4f6c0f398..4df5e5eeada6848cd5669825d3c53ac476569835 100644 (file)
--- a/fs/netfs/objects.c
+++ b/fs/netfs/objects.c
@@ -76,6 +76,7 @@ static void netfs_free_request(struct work_struct *work)
 {
        struct netfs_io_request *rreq =
                container_of(work, struct netfs_io_request, work);
+       unsigned int i;
 
        trace_netfs_rreq(rreq, netfs_rreq_trace_free);
        netfs_proc_del_rreq(rreq);
@@ -84,6 +85,15 @@ static void netfs_free_request(struct work_struct *work)
                rreq->netfs_ops->free_request(rreq);
        if (rreq->cache_resources.ops)
                rreq->cache_resources.ops->end_operation(&rreq->cache_resources);
+       if (rreq->direct_bv) {
+               for (i = 0; i < rreq->direct_bv_count; i++) {
+                       if (rreq->direct_bv[i].bv_page) {
+                               if (rreq->direct_bv_unpin)
+                                       unpin_user_page(rreq->direct_bv[i].bv_page);
+                       }
+               }
+               kvfree(rreq->direct_bv);
+       }
        kfree_rcu(rreq, rcu);
        netfs_stat_d(&netfs_n_rh_rreq);
 }

diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index 3da962e977f5555a519ee4c5c7fecccd84561e53..2bb1273b38f422f2f2e94d794738d63cd76fcb24 100644 (file)
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -190,6 +190,8 @@ struct netfs_io_request {
        struct iov_iter         iter;           /* Unencrypted-side iterator */
        struct iov_iter         io_iter;        /* I/O (Encrypted-side) iterator */
        void                    *netfs_priv;    /* Private data for the netfs */
+       struct bio_vec          *direct_bv;     /* DIO buffer list (when handling iovec-iter) */
+       unsigned int            direct_bv_count; /* Number of elements in direct_bv[] */
        unsigned int            debug_id;
        atomic_t                nr_outstanding; /* Number of ops in progress */
        atomic_t                nr_copy_ops;    /* Number of copy-to-cache ops in progress */
@@ -197,6 +199,7 @@ struct netfs_io_request {
        size_t                  len;            /* Length of the request */
        short                   error;          /* 0 or error that occurred */
        enum netfs_io_origin    origin;         /* Origin of the request */
+       bool                    direct_bv_unpin; /* T if direct_bv[] must be unpinned */
        loff_t                  i_size;         /* Size of the file */
        loff_t                  start;          /* Start position */
        pgoff_t                 no_unlock_folio; /* Don't unlock this folio after read */